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Tunnelling in urban areas by EPB machines: technical evaluation of the system Marilena Cardu, Pierpaolo Oreste Politecnico di Torino, Land, Environment and Geo-Engineering Department, Italy IGAG-CNR, Torino, Italy E-mail: [email protected] ABSTRACT The paper refers to the methods adopted for building a high-speed railway tunnel system between Bologna and Firenze (Italy), focusing attention on the Bologna node which represents the heart of the system, connecting the high speed network’s main lines. The project includes 9 tunnels, accounting for 73 km of the 78 km route crossing below the Apennines. The paper pays attention to the main aspects to be taken into consideration for correctly choosing the tunnel boring machinery (TBM) to be used in urban areas. The fundamental point in analysing technical aspects regarding an earth pressure balance (EPB) machine concerned storing the main excavation parameter values; having collected and organised such data, statistical methods were used for processing it, the instantaneous velocities attained were empirically estimated and idle times were evaluated. The evaluation was made by calculating excavation specific energies (during different excavation phases) to find a satisfactory correlation with the type of ground crossed. Interesting results have been found by comparison with other excavation parameters; in particular, a better understanding of an earth pressure balance shield’s working phases has been reached thanks to an experimental study conducted during the construction of tunnels for a high-speed railway system in Italy. The paper contains details collected regarding the operation of two different EPB machines. RESUMEN Este artículo se refiere a los métodos utilizados para la construcción de túneles para un sistema de trenes de alta velocidad entre Bologna y Firenze (Italia), el punto de interés está sobre el nodo de Bologna, como el corazón de sistema, conectando las líneas principales de la red de alta velocidad. El proyecto incluye nueve túneles, con 73 de los 78 km cruzando por debajo de los Apeninos. Este artículo presenta los principales aspectos a tener en consideración para la correcta selección de máquinas tuneladoras (TBM) utilizadas en las áreas urbanas. El fundamento en el análisis de los aspectos técnicos consiste en un balance de presión de tierra (EPB) de la máquina relacionado a los principales parámetros en la excavación; una vez recogido y organizado los datos, se realizaron análisis estadísticos, se estimaron las velocidades empíricamente y evaluaron los tiempos de espera. La evaluación fue realizada para el cálculo de las energías específicas de excavación (en diferentes fases de perforación) para encontrar una correlación satisfactoria con el tipo de terreno atravesado. Los resultados obtenidos son interesantes en comparación con parámetros de otras excavaciones; en particular, una mejor compresión en el balance de la presión de tierra en cada fase de trabajo, ha sido descrita gracias a un estudio experimental realizado durante la construcción de túneles para un sistema de trenes de alta velocidad en Italia. Este artículo contiene información detallada recogida de la operación de dos maquinas EPB diferentes. Introduction Research instruments’ evolution in the field of tunnel construction has contributed towards the improvement of excavation technologies and planning management, almost during the last 30 years. Excavation techniques’ evolution has also been stimulated by growing urbanisation and the assimilation of the “underground” concept as a space resource, becoming more and more exploitable from various points of view. One of developed countries’ major needs nowadays concerns mobility. Many projects have been promoted during recent years to improve interconnections between European countries. This has involved the problem of tunnelling a great part of the work (Barla G., 1994). The best European example highlighting such need has been the Eurotunnel project which involved constructing three underwater tunnels linking France and the UK. Another important project which is still in execution is the High Speed Railway System; it will Research Groupin Geophysics UNIVERSIDAD NACIONAL DE COLOMBIA EARTH SCIENCES RESEARCH JOURNAL Earth Sci. Res. S J. Vol. 15, No. 1 (July, 2011): 5-11 Keywords: earth pressure balance (EPB), specific energy, excavation parameter, tunnel, tunnelling. Palabras clave: balance presión tierra (EPB), energía especifica, parámetro excavación, túnel. Record Manuscript received: 13/01/2011 Accepted for publication: 15/05/2011 AGOSTO 25-PORTADA GEOCIENCIAS-15-1 2011.prn D:\GEOCIENCIAS JULIO 2011\GEOCIENCIAS 15-1 JULIO 2011.vp jueves, 25 de agosto de 2011 11:28:07 Composite 133 lpi at 45 degrees

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Page 1: Tunnelling in urban areas by EPB machines: technical ... · Tunnelling in urban areas by EPB machines: technical evaluation of the system Marilena Cardu, Pierpaolo Oreste Politecnico

Tunnelling in urban areas by EPB machines: technical evaluation of the system

Marilena Cardu, Pierpaolo Oreste

Politecnico di Torino, Land, Environment and Geo-Engineering Department, Italy IGAG-CNR, Torino, ItalyE-mail: [email protected]

ABSTRACT

The paper refers to the methods adopted for building a high-speed railway tunnel system between Bologna and Firenze(Italy), focusing attention on the Bologna node which represents the heart of the system, connecting the high speednetwork’s main lines. The project includes 9 tunnels, accounting for 73 km of the 78 km route crossing below theApennines. The paper pays attention to the main aspects to be taken into consideration for correctly choosing the tunnelboring machinery (TBM) to be used in urban areas. The fundamental point in analysing technical aspects regarding an earthpressure balance (EPB) machine concerned storing the main excavation parameter values; having collected and organisedsuch data, statistical methods were used for processing it, the instantaneous velocities attained were empirically estimatedand idle times were evaluated. The evaluation was made by calculating excavation specific energies (during differentexcavation phases) to find a satisfactory correlation with the type of ground crossed. Interesting results have been found bycomparison with other excavation parameters; in particular, a better understanding of an earth pressure balance shield’sworking phases has been reached thanks to an experimental study conducted during the construction of tunnels for ahigh-speed railway system in Italy. The paper contains details collected regarding the operation of two different EPBmachines.

RESUMEN

Este artículo se refiere a los métodos utilizados para la construcción de túneles para un sistema de trenes de alta velocidadentre Bologna y Firenze (Italia), el punto de interés está sobre el nodo de Bologna, como el corazón de sistema, conectandolas líneas principales de la red de alta velocidad. El proyecto incluye nueve túneles, con 73 de los 78 km cruzando por debajode los Apeninos. Este artículo presenta los principales aspectos a tener en consideración para la correcta selección demáquinas tuneladoras (TBM) utilizadas en las áreas urbanas. El fundamento en el análisis de los aspectos técnicos consisteen un balance de presión de tierra (EPB) de la máquina relacionado a los principales parámetros en la excavación; una vezrecogido y organizado los datos, se realizaron análisis estadísticos, se estimaron las velocidades empíricamente y evaluaronlos tiempos de espera. La evaluación fue realizada para el cálculo de las energías específicas de excavación (en diferentes fasesde perforación) para encontrar una correlación satisfactoria con el tipo de terreno atravesado. Los resultados obtenidos soninteresantes en comparación con parámetros de otras excavaciones; en particular, una mejor compresión en el balance dela presión de tierra en cada fase de trabajo, ha sido descrita gracias a un estudio experimental realizado durante laconstrucción de túneles para un sistema de trenes de alta velocidad en Italia. Este artículo contiene información detalladarecogida de la operación de dos maquinas EPB diferentes.

Introduction

Research instruments’ evolution in the field of tunnel construction hascontributed towards the improvement of excavation technologies andplanning management, almost during the last 30 years.

Excavation techniques’ evolution has also been stimulated by growingurbanisation and the assimilation of the “underground” concept as a spaceresource, becoming more and more exploitable from various points ofview.

One of developed countries’ major needs nowadays concerns mobility.Many projects have been promoted during recent years to improveinterconnections between European countries. This has involved the problem oftunnelling a great part of the work (Barla G., 1994). The best European examplehighlighting such need has been the Eurotunnel project which involvedconstructing three underwater tunnels linking France and the UK. Anotherimportant project which is still in execution is the High Speed Railway System; it will

Research Groupin Geophysics

UNIVERSIDAD NACIONAL DE COLOMBIA

EARTH SCIENCESRESEARCH JOURNAL

Earth Sci. Res. S J. Vol. 15, No. 1 (July, 2011): 5-11

Keywords: earth pressure balance (EPB), specific energy,

excavation parameter, tunnel, tunnelling.

Palabras clave: balance presión tierra (EPB), energía

especifica, parámetro excavación, túnel.

Record

Manuscript received: 13/01/2011Accepted for publication: 15/05/2011

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provide a more efficient and faster connection amongst European countries. Acritical point has to be resolved when carrying out this work as rail layouts have tocross heavily urbanised areas (Barla G., 2000; Bilotta E. et al., 2002).

Mechanised shields offer a series of advantages and work can be carriedout without having to support the roof. The equipment’s technicalcharacteristics do not represent a basis for effective evaluation because twomechanically identical machines can behave in completely different ways,depending on soil characteristics. It is thus very difficult to make a reliable andunambiguous evaluation of one machine’s best performance compared to thatof another (Bebendererde S., 1995; Bovetti B., 2003). The only way to resolvethis point is to evaluate the equipment’s working parameters during excavation.The most important parameter concerns excavation specific energy which isoften used for determining a machine’s performance (Altindag R., 2003;Copur H. et al., 2003; Cardu M. et al., 2006; Tardaguila I. et al., 2007; AcarogluO. et al., 2008; Exadaktylos G. et al., 2008).

Defining the excavation specific energy concept

Excavation specific energy (ES) represents the amount of energy(expressed in MJ) needed to excavate a unit volume of ground (RostamiJ.,Ozdemir L., 1993; Friant J.E., Ozdemir L., 1993). This may be given by:

EW t

Vs

tot��

(1)

where Wtot is total power, t is excavation time and V is excavated volume.The shield’s feed motion and the head’s rotation speed must be taken into

account when evaluating energy consumption due to the excavation of a unitvolume of ground. The general formula for calculating total excavation specificenergy is given by the sum of these two contributions.

Feed motion contribution

The parameters for calculating a machine’s feed motion are:• The thrust exerted by hydraulic jacks S• A machine’s advancing speed v• Excavation time t.Tunnel diameter must be known, as this is used to calculate a tunnel’s

cross-section. The power needed for a machine’s advance (Wadv) can then beobtained by using the following expression:

W S vadv� � (2)

The rate of excavated volume per time unit is:

V A v t� � �( ) (3)

where A is a tunnel’s cross-section and product v�t represents advance madin time t. Equation (1) can thus be written for feed motion specific energycontribution (ES adv), as:

EW t

V

S v t

A v t

S

AS adv

adv���

� �

� �� (4)

Rotation specific energy

The data needed for calculating rotation are:

• The torque necessary to rotate head C

• The head’s rotation speed ù

• TBM advance speed v.Rotation power (Wrot) is given by:

W Crot � �� (5)

Excavation specific energy consumed by head rotation (ES rot) is thus:

EW t

V

C t

A v t

C

A vS rot

rot���

� �

� ��

� �(6)

Total specific energy

This represents a machine’s behaviour in terms of non-uniformprogression.

Equation (7) is obtained by substituting (1) in equations (4) and (6) (TealeR., 1965):

E E ES

A

C

A vS tot S adv S rot. . .� � � �

���

(7)

It should be noticed that total excavation specific energy is expressed by aformula which does not include time as a variable; it can thus be considered afeature characterising excavation in the stretch which has been calculated fromthe machine’s parameters. Moreover, it can be observed that energy, as wouldbe expected, grows with thrust, torque and rotation speed; excavation difficultyincreases as these three factors also increase. Excavation specific energyobviously decreases as progression speed increases.

Analysis of field performance data and Discussion

The following considerations were based on data collected whenhigh-speed tunnels in the Bologna node excavation were being cut by twoidentical EPB TBMs (Cicala T., 2003; Guidarelli D., 2005). Table 1 gives themachines’ main characteristics.

The first machine (EPB1) worked at advanced chainage (about 1,500 m)compared to the other one (EPB2). It is very important when analysing data totake into account the kind of ground in which work is being done. Excavationspecific energy shown in the following graphs has been represented as afunction of route chainage to facilitate correlation with different types ofground identified by geological characterisation.

EPB1 Es is represented in Figure 1; it varies from a minimum value ofaround 15 MJ/m3 to a maximum of 40 MJ/m3.

Several types of ground are present in this range, particularly:• Clay, from 1,500 m to 1,800 m chainage• Moist sand, from 1,800 m to 2,100 m• Dry sand, from 2,100 m to 2,400 m• Dry gravel, from 2,400 m to 2,700 m.

A negative Es gradient was envisaged from 1,500 m to 2,100 m because of amachine’s progressive adaptation to local ground conditions. Crossing fromclay to sand around 1,800 m chainage was confirmed by decreasing Es (amachine’s adaptation to lithological crossing). Sands were initially on the crownand their presence increased as excavation progressed, making excavationconditions become worse, thereby stressing the need for a machine to becomesuitable to different kinds of ground. This was not observed on contact between

6 Marilena Cardu, Pierpaolo Oreste

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moist and dry sands (around 2,100 m chainage) where a clear increase in Es wasenvisaged. Dry sands, being more compact than moist sands, would require agreater effort to be removed.

Sampling was not regular from 2,100 m to 2,350 m chainage due to someof the machine’s sensors malfunctioning; only a net increase in energy wasidentifiable (but it was impossible to establish whether such evaluation wascompletely reliable). Sampling worked regularly again from 2,350 m. Thisstretch crossed gravels and contact was not abrupt.

Table 1: Specifications for the EPB Lovat RME370SE used in the

Bologna node

Excavation diameter 9.4 m

EPB length + back–up 180 m

EPB weight + back–up ~990 t

Theoretical maximum progression

speed8 cm/min

Minimum bend radius 250 m

Total thrust capacity 10,197 t

Total power 5,100 kW

Torque (standard conditions) 1,022 t·m at 1.97 rpm

Maximum torque 2,043 t·m at 0.98 rpm

Peak torque 2,452 t·m

Standard cutting power 2,700 kW

Analogous considerations could be made for EPB2 excavation. Figure 2shows that Es values were lower than those for EPB1; this clearly stood out bycomparing both machines’ performances at the same chainage (Figure 3).Unfortunately, the data for EPB2 was only available for chainage between 1,500m and 2,050 m.

The phenomenon could have been due to stress release in the ground; thefirst tunnel (cut by EPB1) was excavated between gravels and sands, leading togradual adaptation by the machine, confirmed by a negative Es. gradient.

The original stress distribution of the ground was modified as the secondtunnel (cut by EPB2) was excavated in close proximity to the first one (less thanone diameter), resulting in reduced Es. The decrease in Es was evaluated as beingabout 30%.

This result could also have been related to reduced ground strength due toEPB1 tunnel excavation; however, no data was available regarding themechanical characteristics of the ground measured on site during theexcavation to confirm this hypothesis.

Table 2 shows the main ranges of Es values obtained in different kinds ofground for both EPB1 and EPB2.

Tunnelling in urban areas by EPB machines: technical evaluation of the system 7

Figure 1. EPB1 excavation specific energy

Figure 2. EPB2 excavation specific energy

Figure 3. Comparing EPB1 and EPB2excavation specific energies

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Table 2. Ranges of excavation specific energy values in different kinds

of soil

Type of soil Excavation specific energy (MJ/m3)

Clay 25-35

Moist sand 25-30

Dry sand 32-38

Dry gravel 15-25

Excavation specific energy compared to progression speed

Progression speed is one of the most important parameters whenanalysing the excavation cycle (Innaurato N., 1990; Kovàri K., 2002).

Figure 4 compares the Es with EPB1 instantaneous progression speed atdifferent chainages. According to equation (7), progression speed was inverselyrelated to Es, which was made evident by the plot (increased velocity coincidedwith decreased Es). This was fully in line with the pertinent literature (GrahamP.C., 1976; Nielsen B., Odzemir L., 1993; O’Rourke J.E. et al., 1994; Rostami J.,1997; Thuro K., Plinninger R.J., 2003; Gong Q.M., Zhao J., 2009).

The two graphs’ normalised gradients were similar, apart from theopposite sign. This was expected because the change in speed obtained fromthe pushing jacks’ extension represented the effect of lithological variation(Lovat R. et al., 2001).

Increased energy and decreased speed indicated greater resistance toexcavation by the ground.

Excavation specific energy compared to torque

Figure 5 compares Es to torque at different chainages for EPB1. A directcorrelation was apparent, as expected from equation (7), where the termdirectly proportional to torque prevailed. The correlation was confirmed by theplot and the gradient was similar for both variables. Since EStot was mostlydependent on rotational specific energy (specific energy due to thrust is smaller

and is usually ignored) and torque was a function of the cutting force acting onthe cutting tools, then such direct correlation would be expected (Nielsen B.,Odzemir L., 1993; US Army Corps of Engineers, 1997; Boniface A., 2000;Gong Q.M. et al., 2007).

Excavation specific energy compared to rotation speed

Figure 6 shows the roughly constant value for rotation speed at differentchainages compared to Es variations for EPB1. Rotation speed and torque wereroughly proportional to Es and, as rotation speed was kept practically constant,energy was only affected by torque changes during excavation.

Es variation associated with rotation speed constancy showed that thelatter was the externally controlled variable. An operator could set a constantlevel of rotation speed to maintain constant tool wear, while torque wouldchange to cope with resistance to excavation produced by ground changes. Onthe other hand, if rotation speed were increased, then instantaneouspenetration would decrease, and thus both the cutting force acting on the toolsand torque would decrease.

8 Marilena Cardu, Pierpaolo Oreste

Figure 4. Comparing EPB1 excavation specific energies with instantaneousprogression speed

Figure 5. Comparing EPB1excavation specific energies to torque

Figure 6. Comparing excavation specific energies and rotation speed

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Excavation specific energy compared to total thrust

Figure 7 compares Es to thrust at different chainages for EPB1. Accordingto equation (7), total specific thrust (thrust per unit cross-section) coincidedwith specific advance energy and was added to specific rotation energy, to givetotal Es.

Thrust (as rotation speed) could be controlled by an operator and totalthrust plot was scarcely correlated to total Es plot, apart from some excavationspecific energy peak having some counterpart in thrust peaks, probablyrepresenting attempts by an operator to raise progression speed in difficultground (Lovat R. et al., 2001; Mair N., 1997).

Figure 8 gives specific thrust energy, specific rotation energy and total Es

(thrust energy was a small fraction of total energy).Energy values were calculated statistically by the moving average method,

assuming 60 m progression steps.Figure 8 shows that rotation specific energy was comparable to total Es

throughout the chainage. Only rotation specific energies’ contribution wouldthus be considered in the following.

Suggested evaluation methodology

Rotation speed (as shown in Figure 6) made a very low contribution sinceit was kept almost constant by the operator. The most important parameters tobe considered when calculating excavation specific energies were thus torque(which is a function of rotation speed, as in equation (5)) and progression speed(Marcheselli P.P. et al., 1995; Schmalzbauer S., 1984).

Knowledge of progression speed is determinant during mechanisedfull-section tunnel excavation to evaluate a machine’s performance in real timeor at the end of a shift and to improve (if necessary) its performance regardingoperator intervention related to inspectable parameters.

Obviously, if progression speeds were known (at least regarding ameaningful sample of excavated length), it would become possible to optimisea machine’s work and increase overall excavation time.

It has been previously stated how little influence jack thrust has onevaluating total Es. Equation (7) can thus be simplified as:

EC

A vs �

���

(8)

Equation (8) shows that energy mainly depended on two parameters(torque and progression speed) by assuming constant rotation speed ù.

The following equation was obtained by multiplying excavation specificenergy by tunnel cross-section A:

E AC

vs � �

��

�� (9)

á was expressed in MJ/m. Equation (9) showed good correlation betweenEs and coefficient á.

The example in the graph shown in Figure 9 referred to a 35 MJ/m3Es

value, supplying a 2,360 MJ/m á coefficient.Therefore, if:

��

���

C

vtcos (9’)

then:

C v� � �� � (10)

Tunnelling in urban areas by EPB machines: technical evaluation of the system 9

Figure 7. Comparing EPB1 excavation specific energies to thrust

Figure 8. Comparing EPB1excavation specific energies separately due to rotationand progression speeds Figure 9. Correlation between excavation specific energy and á coefficient

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Hence:

vC�

��

�(11)

Equation (11) shows that torque and progression speed wereproportional dimensions, if rotation speed were considered as a constant.

Maximum torque is the most important parameter to be consideredwhen making a decision during tunnel design stage for evaluating the mostsuitable type of machine. Maximum torque data was provided by the TBM

manufacturer.The graph in Figure 10 gives an example of progression speed evaluated

from torque data for EPB1. Assuming 2,500 t.m average torque at TBM cutterhead and 1 rpm rotation speed, then a 1.05 mm/s net progression speed wouldbe obtained as a reliable average value.

Analysis of a machine’s work performance can be gone into in moredepth, leading to obtaining more accurate predictions. TBM work cyclically,through a sequence of well-defined elementary steps, requiring preciselyknown time intervals.

Each cycle consists of an excavation stage (with a machine advancingthrough the thrust of the jacks), a support erection stage (where a new liningring is installed) and idle time devoted to maintenance.

The sum of lining erection times and maintenance time represents theinactive time between successive ring installations and is repeated at each ring.

At the end of a shift, therefore, elapsed excavation time is much shorterthan total elapsed time. The ratio between the actual excavation time and totaltime, given by:

��T

Texc

total

(12)

represents a machine’s exploitation coefficient (machine utilisation time).When ç and instantaneous progression speed are known, a machine’s

daily (24 hours) progression can be calculated as:

v T vday total inst� � � �� 3 6. (13)

where vday is daily advance rate (m/d), Ttotal is total working time(hours/day) and vinst is the net advance rate (mm/s).

Exploitation (machine utilisation time) coefficient ç is obviously notknown a priori. In the given example this has been calculated by solving the

equation for ç, daily progression speed being known as it can be obtained frommeasured daily advance. However, this only gives a machine’s utilisation timefactor; every contractor should predict this factor based on experience, aparticular project site and conditions prior to construction activity.

Instantaneous progression speed can be obtained by averaging the datastored in a machine’s databank files for the 24-hour period being considered.This would then give:

��� �

v

T v

day

total inst 3 6.(14)

The average progression speed calculated for both EPB1 and EPB2 was0.99 mm/s; a 0.157 exploitation coefficient was then found from these values,meaning that 15.7% of total 24 hours/day working time had been spent in pureexcavation.

Total time was assumed to be 24 hours and, from the exploitationcoefficient, a 3.8 hours/day excavation time was thus calculated. Total inactivetime thus amounted to 20.2 hours/day; this was a very high value, showing theneed for optimising working stages.

By dividing the 20.2 hours by the number of rings, it was found that thetime elapsed was 2.2 hours between the end of the erection of a ring and the startof the erection of the next one. Part of this time was spent on assembling thering, which takes about 40 min, and the remaining part was consumed inordinary maintenance, including time spent waiting for the hardening of themortar that connects the segments of the ring and maybe some otherbreakdowns.

The results are shown in Table 3.

Table 3. Mean daily advancement rate values obtained with 9

rings/day for EPB1

Mean daily progression, m 13.5

Mean instantaneous speed, mm/s 0.99

Working hours in a day 24

Exploitation coefficient ç 0.157

Pure excavation time, hours 3.8

Total inactive time, hours 20.2

Time to assemble a ring, min 40

Maintenance time, hours 14.2

Mean maintenance time/ring, hours 1.58

Conclusions

Comparing the most important excavation parameters led to interestingresults for better understanding of earth pressure balance shields’ workingphases.

In particular, the following considerations should be highlighted:• Excavation specific energy Es did not appreciably depend upon thrust;

rotation velocity too, being constant during drive, did not seem tosubstantially influence evaluation of excavation specific energy;

• Excavation specific energy Es was directly correlated to torque;

10 Marilena Cardu, Pierpaolo Oreste

Figure 10. Correlation between torque and progression speed

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• Ground stress release appreciably modified excavation specific energyvalues. In this case, this was the excavation of a second tunnel bymachine EPB2 at a distance of less than one diameter from the firsttunnel which had already been built by EPB1, occurring with a 30% Esreduction;

• Excavation specific energy Es varied widely with groundcharacteristics: a large variation in excavation specific energy rangeswas in fact observed as a function of the subsoil encountered, from25-35 MJ/m3 for clay, to 15-25 MJ/m3 for dry gravel, to 32-38 MJ/m3

for dry sand; and• Exploitation coefficient ç was low and varied from 0.10 to 0.20 for the

project being analysed.Progression speed was one of the main parameters to be considered

during excavation. Regarding this point, an interesting method could besuggested, namely automatic continuous diagraphy (DAC).

Through an appropriate scale factor it enables estimating a givenmachine’s daily progression speed (progression speed having already beendefined) to establish the necessary torque C to be applied by a tunnellingmachine.

References

Barla, G. (1994): “Scavo di gallerie in prossimità della superficie”. V Ciclo di conferenze diMeccanica e Ingegneria delle rocce (MIR). Torino.

Barla, G. (2000): “Lo scavo meccanizzato delle gallerie”. VIII Ciclo di conferenze diMeccanica e Ingegneria delle rocce (MIR). Torino.

Bilotta, E., G. Russo and C. Viggiani (2002): “Cedimenti indotti da gallerie superficiali inambiente urbano”. XXI Convegno Nazionale di Geotecnica: Opere geotecniche inambiente urbano. L’Aquila.

Bebendererde, S. (1995): “Advanced techniques for EPB-TBM operation”. Tunnel etouvrages souterrains, 128.

Bovetti B. (2003): “Studio della subsidenza indotta dallo scavo meccanizzato dellaMetropolitana di Torino attraverso modellazione numerica e back-analysis”. Tesidi Laurea, Politecnico di Torino, Torino.

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